+7 mph by fixxing poor quality on 66cc

Discussion in 'Motorized Bicycle General Discussion' started by Motorbikermark, Dec 18, 2011.

  1. Motorbikermark

    Motorbikermark New Member

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    I've been breaking in my 1st MB build and as I have done in past auto or motorcycle project I do a basic break down just to make sure no major issues. So this is what I found.

    1) I noticed a little blow by on the fins around the head. I came to the conclusion that the studs were a tad long and the accorn nuts were bottoming out. (would have liked to check compression before and after, But I no longer own the tools for this. Which is why I love motorbikes, No need for a Snap on tool box and $4000 in tools) (Fix) trimmed the studs down 1/8th of an inch.

    2) Took off the carb, found that the the carb did not slide all the way back on intake. creating a leak in the slots under the retaining band. (Fix) used dremel to sand away burr on the mating surface. Make sure to block opening to venturi and float bowl.

    3) Removed intake, found gasket damp and stained suggesting a leak. noticed that the nut and washers were not able to sit even on the intake due to large sloppy welds. (probably wouldn't affect performance but looked unprofessional if nothing else) also decided that those studs also were too long to allow accorn nuts to properly tighten. (fix) Trimmed down studs and grind welds making sure not to get too close to base of intake.

    4) Intake needed porting and polishing really bad! (Fix) give her what she needs! Used dremel to remove slag and burrs from inside of intake. Polished using 300 grit wheel.

    5) Found replacement gasket did not match intake. (Fix) Mated gasket to intake and sanded gasket even using dremel.

    6) Compared sanded gasket to intake port, Found rectangler intake port looked good but blocked part of the opening of the gasket (intake). (fix) Block the intake port mate gasket up, used dremel to taper back the extra material on the intake port. Clean port using rag damp with alcohol then with a magnet.

    7) Exhaust gasket did not mate up. (Fix) Sand gasket even using dremel.

    After what I found just from a basic tear down I am seriously considering a complete tear down. I must say the clutch appeared good as did the magneto. Before the fixxes with a 41 tooth sprocket I was running just shy of 27mph (according to my garmin GPS) after I ran a good 35mph. I would like to say that none of these issues are anything that I would consider inapproperate based on the price of these kits. I am a machine operator for a company that produces brake calipers and if these kits were manufactored to the level needed they would be double if not more in price, And lets face it we love working on our bikes! If these kits were super high quality there wouldn't be anything for us to fix or improve. What fun would it be if you threw together these things in 2hrs then never had to touch them again. I do think that next time I will also do a pre-tear down. Let me know what you have found as a result of you working on these fun little machines.

    God Speed, Mark.bld.
     
  2. leadfarmer

    leadfarmer New Member

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    Oh yeah, I spent a day doing these joyful things a couple of weeks ago.
     
  3. DaveC

    DaveC Member

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    I think you'll find that the studs arn't too long, it's that the Chinese don't always tap the holes to the bottom. I think to cut labor costs even further than it is. Metric tap set at Harbor Freight is less that $13 and a good investment with these motors.
     
  4. Allen_Wrench

    Allen_Wrench Resident Mad Scientist

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    These little HT motors really are great, once you get done "blueprinting" and port matching and detailing and troubleshooting and...
     
  5. Motorbikermark

    Motorbikermark New Member

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    I'm thinking I may replace all the studs and screws with hardened steel hex bolts. Would look trick wouldn't worry about stripping philips head screws, and no length issues or thread depth issues.
     
  6. Fulltimer

    Fulltimer New Member

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    My motor was slightly used when I got it. Only a few hours. But I think this winter I'll take her down and fix all the "little things" that were done wrong. Or should I say not done at all? If it were not for my bike I would be in the house all the time and irritating my wife!! See, they are GOOD for a marriage!

    Terry
     
  7. F_Rod81

    F_Rod81 Dealer

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    I agree...

    Once these motors are gone through with a fine comb and tuned properly, they can easily see 5000+ miles or lots more. It all depends on the owner. Good to hear that some old tricks worked for you. (^)
     
  8. DaveC

    DaveC Member

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    They are a little spendy but not too bad but sick bike parts has Allen-head cap screws in a kit all ready to go. With the countersunk holes on these motors a hexhead bolt would ride on the surface of the housing and would have very poor sealing properties. On intakes and exhausts you get a little more clearance for the bolthead. Tapping the holes really needs to be done if either type of bolt is used.
     
  9. sputterputtBAM

    sputterputtBAM New Member

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    I had clearance on the counter sink of engine case and covers for hex head.(shrug)
    I chose not to replace studs with hex head as I don't feel it's good to pull a bolt in\out of the alum. when repairing\adjusting.
     
  10. edangel

    edangel New Member

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    ok i know a while back some one did a light off the white wire of the motor i just got a bullet light and put it on my bike and ran a nuber 10 wire up to the light switch and added a ground wire the light come on for about 5 min then gose out the bulb is a 2.2 v its saids on the side if i got to do more please some one let me know
     
  11. thegnu

    thegnu New Member

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    do the total teardown I found moderate "crap " in mine an many other members have found much worse .
    Gary
     
  12. maintenancenazi

    maintenancenazi New Member

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    ^^ This. The reports of all kinds of nasty stuff found in these engines (including my own) are too many to list. I consider it MANDATORY to do a full tear down, and inspection of every motor that you receive, before ever putting it into service. It's just cheap insurance.

    Even still, after tearing down and cleaning, fixing threads, ect. I still had my first one go south after only 5 minutes of running! Turns out the main bearings completely self destructed, ( one side even spun in the case! )

    I'm still going to try and rebuild this engine, so hopefully I'll at least have a spare when this new one expires. It truly [email protected]#ks when....:-||
     
    #12 maintenancenazi, Dec 19, 2011
    Last edited: Dec 19, 2011
  13. 2door

    2door Moderator
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    The OP did many things that need to be done. My suggestion would be to get rid of those pretty acorn nuts and replace with shouldered hex nuts. Also he should not rely on a metal to metal seal at the carburetor/intake manifold. A good gasoline resistant sealer should be used at that point. I like SealAll as opposed to most of the silicone based sealers which are not gasoline compatible.

    The welds on the intake and exhaust flanges have always been a problem and should be ground away to allow proper seating of the fasteners.

    Sounds like he'll have a reliable installation if he pays the same attention to the other parts of his install.
    Tom
     
  14. Motorbikermark

    Motorbikermark New Member

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    Thanks Tom it helps to have a vote of confidence from someone with more experience with these things.
     
  15. rustycase

    rustycase Gutter Rider

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    Yup.
    I am still running the acorn nuts, and have only checked them for tight a few times...
    When I get to some point where I must take them off I will replace them because the metal they are made from is suspect. 8.8 grade ss is probably the way to go.
    Best
    rc
     
  16. KCvale

    KCvale Active Member

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    First things first, nice job spotting all the 'always check' things when building a 2-stroker, it takes most people a few builds to find them.

    What you haven't learned with your first build yet is all motor kits are not the same so you need to specify the exact year, make and model of the motor you refer to as not ALL these motors are 'poor quality'.

    I only use Skyhawk motors and it only takes me 1/2 an hour to prep one.

    I use an angle grinder on the outside of intake/exhaust flanges to flatten it and remove any weld that keeps the washers from sitting flat, use a rasp bit on my drill to clear out any crap on the port pipes insides, torque the head bolts, set the spark plug gap if not simply replace it with an Iridium one, and then pop the right side clutch cover to make sure the freewheel bearing is not dried hard and stuck.

    If it's a 66cc with a CNS carb I also gasket seal the grove on the top to prevent air leaks there and let it cure over night.

    As far as 'cracking the case' to inspect the main bearings on every new motor, well to me that is just silly for lack of better friendly term.
    Suggesting a layman even pull the cylinder off is likely to leave them with problems they didn't have to start with, let alone cracking the case, though I usually pop the head off to reverse the orientation of the slat heads and inspect the gasket.

    Anyway...
    It's always nice to get a new experienced mechanic in here and you sound like a good one so welcome bud, just be mindful that a large portion of the audience here are just kids that don't even have decent tools let alone mechanical skills is all ;-}

    So are you hooked on building more of these yet?
    It still amazes me how far they can be taken so I just keep building them ;-}
     
  17. 2door

    2door Moderator
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    Well said, KC. Thanks for chiming in. I too feel that recommending a complete tear down could be problematic for someone who has little to no experience with the HT. Pulling the cylinder head to check the walls may not be a bad idea. It should be stressed that removing the head will allow unseating the base gasket so care should be taken when doing it. I also believe that simply rotating the crankshaft a few times to check for binding or foreign objects could prevent some trouble.
    Tom
     
  18. Motorbikermark

    Motorbikermark New Member

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    Thanks guys, I had decided that though there might be a chance of internal debris that a tear down at this point (150 miles in to break in) could cause more problems than fixes. Being its not a wet lube system the chances are that any debris will just sit at the bottom of the crankcase. I decided to replace the 415 chain with a #41 since I'm going to be playing with gear ratios and I don't want 4 chains at $15 a pop laying aroung or have to wait a week everytime I need a half link. Do any of you see an issue with this? Theres probably a load strength difference but I believe it would favor the #41 anyway. Plus I don't plan on riding any fat chicks on it anyway. Once again thanks for all your input its appreciated.

    God Speed, Mark
     
  19. Cavi Mike

    Cavi Mike New Member

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    The leaking carb/manifold is a common and well-known issue and it's easily remedied by a simple o-ring placed inside the manifold. I'm sure all of the port-matching and everything you did netted you some gains but fixing that leak is the biggest problem with these engines. I'm honestly really surprised they haven't started including an o-ring with the kit considering how much other extra stuff they give you.
     
  20. maintenancenazi

    maintenancenazi New Member

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    I don't think you will go wrong with a #41. When I upgraded mine to this, I could tell a huge difference in the smoothness of the drive train. It's well worth it!

    Peace, James
     

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